1. Field of the Invention
The present invention relates to a hot-plug signal detecting apparatus that detects a hot plug signal outputted from a sink device or a repeater device, and the source device and the repeater device that comprise the hot-plug signal detecting apparatus.
2. Description of the Related Art
In recent years, an AV system made of a source device that supplies contents data such as video data and audio data, and a receiving device such as a sink device and a repeater device that receives the contents data has been spread. The source device is, for example, a DVD (Digital Versatile Disk) player, BD (Blue-ray Disc) player, HDDVD (High Definition DVD) player, CD player or the like. The sink device is, for example, an LCD (Liquid Crystal Display), PDP (Plasma Display Panel), projector or the like. The repeater device is, for example, an AV amplifier, AV receiver or the like. These devices comply with HDMI standards, and are mutually connected through an HDMI cable.
To explain a case where a PDP, which is a sink device, and a DVD player, which is a source device, are connected as an example, the DVD player includes a hot-plug signal detecting apparatus that detects a hot plug signal outputted from the PDP. When a setting change (for example, stand-by, switching of a selector, disconnection of an HDMI link or the like) is notified, the PDP inverts the hot plug signal from a high level to a low level, and then again inverts it to the high level. When the hot plug signal is inverted to the low level, the DVD player executes cutting processing of the HDMI link, and when it detects the inversion to the high level, realizes the change of the setting of the PDP, acquires various pieces of information (for example, EDID or the like) from the PDP, makes setting of the HDMI, and executes necessary processing such as establishment of the HDMI link.
FIG. 5 is a block diagram showing a conventional hot-plug signal detecting apparatus of a DVD player. A transmission processing unit 41 converts video data and audio data read from a DVD disk by a drive not shown in the figure to data compliant with an HDMI standard (hereinafter, referred to as HDMI data), and transmits it to a PDP through a TMDS channel.
Furthermore, the transmission processing unit 41 is connected to a connector 44 through a hot-plug detecting circuit 43 and resistances R28, R29. When a hot plug signal outputted from the PDP is inverted from a high level to a low level, the hot-plug detecting circuit 43 detects that the hot plug signal has been inverted to the low level, and outputs the hot plug signal of the low level to a hot-plug input terminal HPDin of the transmission processing unit 41. The transmission processing unit 41 detects that the hot plug signal has been inverted to the low level based on the hot plug signal inputted to the HPDin, and executes necessary processing.
The high level of the hot plug signal is 2.0 to 5.3 V, the low level is lower than 2.0 V, and these voltage values differ depending on a sink device. In the transmission processing unit 41, a predetermined binary hot plug signal of the high level or low level needs to be inputted to the hot-plug input terminal HPDin so that the high level or the lower level of the hot plug signal can be detected. Therefore, necessary is the hot-plug detecting circuit 43 that detects whether the voltage of the hot plug signal is in a high level range or in a low level range and outputs the predetermined binary hot plug signal of the high level or low level to the transmission processing unit 41, in order that the transmission processing unit 41 can detect the high level or the low level whatever voltage of the hot plug signal is outputted from the connected sink device. The hot-plug detecting circuit 43, as shown in FIG. 6, is made of an inverter circuit.
The transmission processing unit 41 is made of an MPEG chip, and needs to execute various processings such as control of the drive, decoding processing of MPEG data read from the DVD disk, and communications with a controller 42, in addition to the processing of inverting the contents data to the HDMI data. Accordingly, the parallel execution of a plurality of processings largely increases load on the transmission processing unit 41. Therefore, for the purpose of reducing the load, an interval (cycle) at which the hot plug signal inputted to the hot-plug input terminal HPDin is detected is set to be large. For example, the cycle of detection of the hot plug signal is set to 200 ms. In this case, if the sink device outputs the hot plug signal of the low level having a period of 100 ms, the transmission processing unit 41 can fail in detecting that the hot plug signal has been inverted to the low level. If the change of the hot plug signal cannot be detected, there arise problems that the operation based on the HDMI standard cannot be precisely executed, so that the contents data cannot be transmitted between the sink device and the source device, that various settings cannot be reflected, and the like. Furthermore, if the transmission processing unit 41 detects the hot plug signal with a short cycle, the above-described problems can be solved, while the problem that the load on the transmission processing unit 41 is increased is posed.
Moreover, in the case where a PDP which is a sink device and an AV amplifier which is a repeater device are connected, the AV amplifier includes a hot-plug signal detecting apparatus that detects a hot plug signal outputted from the PDP to detect the hot plug signal as described above.